1. Field of the Invention
The present invention relates to motorized power equipment and more specifically to a hydraulic drive system for motorized power equipment.
2. Description of Related Art
With the advent of motorized power equipment, various ways of propelling the power equipment have been developed. For example, early self propelled lawn mowers employed gear driven transmissions. In these lawn mowers, the drive shaft of the motor would provide power to a transmission which directs power to an axle or drive shaft of the wheels. Similar to a car, the speed of the propulsion system is dependant upon the gear used.
Over time, hydrostatic transmissions were used as an intermediate stage between the drive shaft of the engine and the wheels. Within hydrostatic transmissions, hydraulic pumps were used to provide the rotational energy to the drive systems. Powered lawn equipment typically needs the engine to operate at full speed at all times to not only operate blades of a mower, but also provide energy to drive the lawn mower. Hydrostatic transmissions receive the constant energy from the engine and provide variable output speeds.
Hydraulic pumps are typically engaged by a belt which is linked back to the drive shaft of the engine. As the drive shaft of the engine turns, the drive belt turns the hydro input and hydraulic fluid pumps. Even though fluid may be pumping within the hydraulic pump, pressure does not build until a swash plate is tilted. The direction the swash plate is tilted controls the rotational direction of the output shaft (forward and reverse). In addition, the amount of tilting that the swash plate experiences determines the rotational speed applied to the wheels of the lawn equipment. The greater the degree of displacement or tilt, the higher the output speed. While the engine is turning and as the swash plate tilts, pistons within the hydraulic pump begin to pump fluid which in turn rotates an output drive shaft. The output drive shaft of a hydraulic pump tends to rotate quickly but with relatively low torque. In prior art drive systems, the output drive shaft has various gear assemblies attached thereto allowing the appropriate amount of torque to be applied to the drive assemblies. The drive assemblies are typically attached to a wheel or set of wheels. Thus, as the engine drive shaft turns, the hydraulic pump circulates hydraulic fluid which rotates the output drive shaft and the wheel or wheels turn. Those skilled in the art appreciate that the output speed of the hydraulic motors may be varied by controlling the volume of fluid being pumped through the hydraulic motor.
One drawback of the prior drive systems is the lack of flexibility of the placement of the propulsion systems. For example, the output drive shaft of a hydraulic motor would have gears or a gear train attached and any wheel attached would be fixed into place by the gearing assemblies. Essentially, the gears extend radially away from the output drive shaft and if a different size wheel was required, a whole new gear system would need to be implemented. Alternatively, even if the gearing was acceptable, any change in chassis's height presented the need to redesign the gears or gearing assembly. In addition, should different gear ratios be required, an entirely new gear assembly and housings would need to be designed and implemented into the power equipment or worse, a total redesign of the lawn equipment would be necessary. There is typically no way of changing the gear ratios in the field by replacing one gear.
In most power equipment assemblies, there is very little room under the chassis for all of the drive mechanisms. As a result, power equipment manufacturers may find it advantageous to be able to move the wheel hub assembly away from the hydraulic motor. The present invention allows the wheel hub to be attached to the hydraulic motor via a rotational drive assembly. This also allows the output drive of the propulsion system to be located outside the confines of the chassis, thus eliminating clutter and freeing up space. The rotational assembly may have a replaceable receiving pulley that may be changed in the field. By changing the diameter of the receiving pulley, the drive ratio of the propulsion system may be changed. In addition, by using the various aspects of the present invention, the wheel hub may be located in different locations under the chassis, so long as the rotational drive assembly may connect to the output drive shaft of the hydraulic pump. In addition, the wheel hub of the present invention may be mounted on the outside of the frame, thus moving the wheel hub out from inside the chassis area.